When the speaker size is set to large the 970 sends a full bandwidth signal to the speakers, thus no crossover. If you want a crossover then you have to set the speaker size to small. I don't imagine the Polks will have a problem accepting the full range input but you may want play with it a little and see which you prefer.

I set all the trim levels to '0' and then adjust the main volume knob to get close. I always start with my left front speaker and then match the others to that one. I'm not too picky about the 75dB reading. If it happens to be 72 I just match all the speakers to 72. Sound meter should be at your listening position and remember to use "C" weighting.

Setting the distance won't impact the level readings so setting it before or after doesn't matter.